Management of non-volatile memory systems having large erase blocks

ABSTRACT

A non-volatile memory system of a type having blocks of memory cells erased together and which are programmable from an erased state in units of a large number of pages per block. If the data of only a few pages of a block are to be updated, the updated pages are written into another block provided for this purpose. The valid original and updated data are then combined at a later time, when doing so does not impact on the performance of the memory. If the data of a large number of pages of a block are to be updated, however, the updated pages are written into an unused erased block and the unchanged pages are also written to the same unused block. By handling the updating of a few pages differently, memory performance is improved when small updates are being made.

BACKGROUND

This invention relates generally to the operation of semiconductornon-volatile memory systems such as flash memory, and, morespecifically, to the operation of such memory systems having very largeerasable memory cell blocks and which access the blocks in much smallerunits for programming and reading data.

There are many commercially successful non-volatile memory productsbeing used today, particularly in the form of small form factor cards,which employ an array of flash EEPROM (Electrically Erasable andProgrammable Read Only Memory) cells formed on one or more integratedcircuit chips. A memory controller, usually but not necessarily on aseparate integrated circuit chip, interfaces with a host to which thecard is removably connected and controls operation of the memory arraywithin the card. Such a controller typically includes a microprocessor,some non-volatile read-only-memory (ROM), a volatilerandom-access-memory (RAM) and one or more special circuits such as onethat calculates an error-correction-code (ECC) from data as they passthrough the controller during the programming and reading of data. Someof the commercially available cards are CompactFlash™ (CF) cards,MultiMedia cards (MMC), Secure Digital (SD) cards, Smart Media cards,personnel tags (P-Tag) and Memory Stick cards. Hosts include personalcomputers, notebook computers, personal digital assistants (PDAs),various data communication devices, digital cameras, cellulartelephones, portable audio players, automobile sound systems, andsimilar types of equipment. Besides the memory card implementation, thistype of memory can alternatively be embedded into various types of hostsystems.

Two general memory cell array architectures have found commercialapplication, NOR and NAND. In a typical NOR array, memory cells areconnected between adjacent bit line source and drain diffusions thatextend in a column direction with control gates connected to word linesextending along rows of cells. A memory cell includes at least onestorage element positioned over at least a portion of the cell channelregion between the source and drain. A programmed level of charge on thestorage elements thus controls an operating characteristic of the cells,which can then be read by applying appropriate voltages to the addressedmemory cells. Examples of such cells, their uses in memory systems andmethods of manufacturing them are given in U.S. Pat. Nos. 5,070,032,5,095,344, 5,313,421, 5,315,541, 5,343,063, 5,661,053 and 6,222,762.

The NAND array utilizes series strings of more than two memory cells,such as 16 or 32, connected along with one or more select transistorsbetween individual bit lines and a reference potential to form columnsof cells. Word lines extend across cells within a large number of thesecolumns. An individual cell within a column is read and verified duringprogramming by causing the remaining cells in the string to be turned onhard so that the current flowing through a string is dependent upon thelevel of charge stored in the addressed cell. Examples of NANDarchitecture arrays and their operation as part of a memory system arefound in U.S. Pat. Nos. 5,570,315, 5,774,397, 6,046,935, and 6,522,580.

The charge storage elements of current flash EEPROM arrays, as discussedin the foregoing referenced patents, are most commonly electricallyconductive floating gates, typically formed from conductively dopedpolysilicon material. An alternate type of memory cell useful in flashEEPROM systems utilizes a non-conductive dielectric material in place ofthe conductive floating gate to store charge in a non-volatile manner. Atriple layer dielectric formed of silicon oxide, silicon nitride andsilicon oxide (ONO) is sandwiched between a conductive control gate anda surface of a semi-conductive substrate above the memory cell channel.The cell is programmed by injecting electrons from the cell channel intothe nitride, where they are trapped and stored in a limited region, anderased by injecting hot holes into the nitride. Several specific cellstructures and arrays employing dielectric storage elements aredescribed by Harari et al. in United States patent applicationpublication no. 2003/0109093.

As in most all integrated circuit applications, the pressure to shrinkthe silicon substrate area required to implement some integrated circuitfunction also exists with flash EEPROM memory cell arrays. It iscontinually desired to increase the amount of digital data that can bestored in a given area of a silicon substrate, in order to increase thestorage capacity of a given size memory card and other types ofpackages, or to both increase capacity and decrease size. One way toincrease the storage density of data is to store more than one bit ofdata per memory cell and/or per storage unit or element. This isaccomplished by dividing a window of a storage element charge levelvoltage range into more than two states. The use of four such statesallows each cell to store two bits of data, eight states stores threebits of data per storage element, and so on. The charge level of astorage element controls the threshold voltage (commonly referenced asVT) of its memory cell, which is used as a basis of reading the storagestate of the cell. A threshold voltage window is commonly divided into anumber of ranges, one for each of the two or more storage states of thememory cell. These ranges are separated by guard bands that individuallyinclude a nominal sensing reference level for reading the storage statesof the individual cells.

Multiple state flash EEPROM structures using floating gates and theiroperation are described in U.S. Pat. Nos. 5,043,940 and 5,172,338, andfor structures using dielectric floating gates in aforementioned U.S.application Ser. No. 10/280,352, publication no. 2003/0109093 A1.Selected portions of a multi-state memory cell array may also beoperated in two states (binary) for various reasons, in a mannerdescribed in U.S. Pat. Nos. 5,930,167 and 6,456,528.

Memory cells of a typical flash EEPROM array are divided into discreteblocks of cells that are erased together. That is, the block is theerase unit, a minimum number of cells that are simultaneously erasable.Each block typically stores one or more pages of data, the page beingthe minimum unit of programming and reading, although more than one pagemay be programmed or read in parallel in different sub-arrays or planes.Each page typically stores one or more sectors of data, the size of thesector being defined by the host system. An example sector includes 512bytes of user data, following a standard established with magnetic diskdrives, plus some number of bytes of overhead information about the userdata and/or the block in which they are stored. Such memories aretypically configured with 16, 32 or more pages within each block, andeach page stores one or just a few host sectors of data.

In order to increase the degree of parallelism during programming userdata into the memory array and read user data from it, the array istypically divided into sub-arrays, commonly referred to as planes, whichcontain their own data registers and other circuits to allow paralleloperation such that sectors of data may be programmed to or read fromeach of several or all the planes simultaneously. An array on a singleintegrated circuit may be physically divided into planes, or each planemay be formed from a separate one or more integrated circuit chips.Examples of such a memory implementation are described in U.S. Pat. Nos.5,798,968 and 5,890,192.

To further efficiently manage the memory, blocks may be linked togetherto form virtual blocks or metablocks. That is, each metablock is definedto include one block from each of several or all of the planes. Use ofthe metablock is described in United States patent applicationpublication no. 2002-0099904. The metablock is identified by a hostlogical block address as a destination for programming and reading data.Similarly, all blocks of a metablock are erased together. The controllerin a memory system operated with such large blocks and/or metablocksperforms a number of functions including the translation between logicalblock addresses (LBAs) received from a host, and physical block numbers(PBNs) within the memory cell array. An intermediate quantity of logicalblock numbers (LBNs) may also be used, one LBN typically designating arange of LBAs that include an amount of data equal to the storagecapacity of one or more memory array blocks or of a metablock.Individual pages within the blocks are typically identified by offsetswithin the block address. Address translation often involves useslogical block numbers (LBNs) and logical pages.

In an ideal case, the data in all the pages of a block would be updatedtogether by writing the updated data to the pages within an unassigned,erased block, and a logical-to-physical block number table would then beupdated with the new address. The original block would then be availableto be erased and placed in an erased block pool for future use. However,it is more typical that the data stored in a number of pages less thanall of the pages within a given block must be updated. The data storedin the remaining pages of the given block remain unchanged. Theprobability of this occurring is higher in systems in which the numberof pages of data stored per block is higher. One technique now used toaccomplish such a partial block update is to write the data of the pagesto be updated into a corresponding number of the pages of an erasedblock and then to copy the unchanged pages from the original block intopages of the new block. The original block may then be erased and addedto the erased block pool. Over time, as a result of host data filesbeing re-written and updated, many blocks can end up with a relativelyfew number of its pages containing valid data and remaining pagescontaining data that are no longer current. In order to be able toefficiently use the data storage capacity of the array, logicallyrelated data pages of valid data are from time-to-time gathered togetherfrom fragments among multiple blocks and consolidated together into afewer number of blocks. This process is commonly termed “garbagecollection.”

An alternative technique similarly writes the updated pages to adifferent block than the block containing the original data buteliminates the need to copy the other pages of data into the new blockby appropriately marking the data to distinguish the updated data fromthe superceded data that are identified by the same logical address.This is a subject discussed in afore-mentioned United States publishedapplication no. 2002-0099904. Then when the data are read, the updateddata read from pages of the new block are combined with the unchangeddata read from pages of the original block that remain current, and theinvalid superceded data are ignored.

The memory system controller is preferably able, by its structure andcontrolling firmware, to cause data to be programmed and read under avariety of conditions imposed upon it by the host. At one extreme,audio, video or other streaming data can be received at a high rate ofspeed, and the memory system is called upon to store the data in realtime. At another extreme, the host may cause the memory system tooccasionally program one sector of data at a time or to program severalsingle data sectors together that have non-sequential logical addresses.The same data sector can be also be frequently updated. Such singlesector programming can occur, for example, when a file allocation table(FAT) stored in the array is being written or updated. The problempresented by such operations on large erase block memories is thatfrequent garbage collection is required in order to efficiently utilizethe storage capacity of the memory. The controller needs to suspend itsprimary function of transferring data in and out of the memory in orderto perform garbage collection, thus adversely affecting systemperformance.

SUMMARY OF THE INVENTION

Accordingly, at least two different mechanisms are maintained forprogramming data according to the characteristics of write commandsreceived from a host in order to increase the overall performance of thememory system. In general, the storage of non-sequentially addresseddata is treated differently than the storage of sequentially addresseddata, in ways that optimize memory system performance with either typeof operation.

In an example implementation, a host command to program a single hostunit of data (a sector being a common example), a small number of unitswith sequential logical addresses or units of data with non-sequentiallogical addresses are handled differently than a host command to programa number of data units that is large, relative to the storage capacityof the individual logical blocks or metablocks, and which havesequential logical addresses. The single, small number of sequentialdata units or non-sequential data units are written to a first type ofdesignated logical block or metablock while the larger number ofsequential data units are written to a second type of designated logicalblock or metablock. The first type of designated block or metablock(referenced herein as E1) receives updates of data spread over a widerange of logical addresses while the second type of designated block ormetablock (referenced herein as E2) receives updates of data stored in arange of logical addresses limited to a single block. Further, if asingle or non-sequential data units are more frequently updated thanother data units with surrounding logical addresses, the updates may bestored in the first type of designated logical block or metablock thatis dedicated to the logical address range of those units (referencedherein as dE1).

A principal result of using these designated blocks is a reduction ofthe amount of data consolidation that currently becomes necessary whenless data that may be stored in a block are updated. The updated dataneed not be immediately recombined in a single physical block withunchanged data of the same logical block, thus improving systemperformance. Such a recombination may be postponed until a time when itinterferes less with the memory system's acquisition and storage ofdata. Further, the various designated blocks are preferably dynamicallyformed to accommodate the programming commands being received, therebyto adapt the memory system for high performance operation in a widevariety of data storage applications.

Additional aspects, features and advantages of the present invention areincluded in the following description of exemplary embodiments, whichdescription should be read in conjunction with the accompanyingdrawings. All patents, patent applications, articles publications andother documents referenced herein are hereby incorporated herein by thisreference in their entirety for all purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a typical existing flash EEPROM memorydevice with a memory cell array, control logic, and data and addressregisters;

FIG. 2 illustrates an architecture utilizing several memory devices ofFIG. 1 with a system controller;

FIG. 3 schematically illustrates an arrangement of blocks in two planes,as an example of the memory array of FIG. 1;

FIG. 4 shows an example of one block of FIG. 3 that stores multiplepages 0-15;

FIG. 5 is a representation of a data sector stored in a page of a blockof FIGS. 3 and 4;

FIG. 6 illustrates an existing process of updating data in less than allof the pages of a multi-paged block;

FIGS. 7A and 7B are tables of corresponding logical and physical pageaddresses for the original and new blocks of FIG. 6, respectively;

FIG. 8 illustrates one example of a designation of consolidation blocksE1 and E2 within one plane of the array of FIG. 3;

FIG. 9 provides an example the use of the consolidation block E1 of FIG.8 to update the data in a few of the pages of another block;

FIG. 10 shows an example of data fields within a data sector stored in apage of FIG. 9;

FIGS. 11A and 11B illustrate one example of sequential operations ofconsolidating updated data pages of a given data block that uses theblock E2 but not the block E1 of FIG. 8;

FIGS. 12A, 12B and 12C illustrate one example of sequential operationsof consolidating updated data pages of a given data block that uses bothof the blocks E1 and E2 of FIG. 8;

FIGS. 13A, 13B and 13C illustrate another example of sequentialoperations to update a few pages of data of a given block that uses bothof the blocks E1 and E2 of FIG. 8;

FIG. 14 illustrates another example of a designation of consolidationblocks E1 and E2 within a unit of the array of FIG. 3;

FIGS. 15A and 15B illustrate an example of sequential operations toupdate a few pages of data of a given block that uses both of theconsolidation blocks E1 and E2 of FIG. 14;

FIG. 16 illustrates use of blocks E1 and E2 in a type of memoryarchitecture that stores data in metablocks;

FIG. 17 shows a modification of the memory architecture of FIG. 16 withthe E1 block being a metablock;

FIG. 18 provides an example of the mapping of logical addresses into aset of E1, dE1 (dedicated E1) and E2 blocks;

FIG. 19 is a flow chart showing operation of the memory system of FIGS.1-5 in response to host write commands that uses consolation blocks E1,dE1 and E2; and

FIG. 20 is a flow chart showing the steps taken in the process of FIG.18 to allocate any of the E1, dE1 or E2 blocks.

DESCRIPTION OF EXISTING LARGE BLOCK MANAGEMENT TECHNIQUES

FIG. 1 shows a typical flash memory device internal architecture. Theprimary features include an input/output (I/O) bus 411 and controlsignals 412 to interface to an external controller, a memory controlcircuit 450 to control internal memory operations with registers forcommand, address and status signals. One or more arrays 400 of flashEEPROM cells are included, each array having its own row decoder (XDEC)401 and column decoder (YDEC) 402, a group of sense amplifiers andprogram control circuitry (SA/PROG) 454 and a data register 404.Presently, the memory cells usually include one or more conductivefloating gates as storage elements but other long-term electron chargestorage elements, including a charge trapping dielectric, may be usedinstead. The memory cell array may be operated with two levels of chargedefined for each storage element to therefore store one bit of data witheach element. Alternatively, more than two storage states may be definedfor each storage element, in which case more than one bit of data isstored in each storage element.

If desired, a plurality of arrays 400, each with its associated Xdecoders, Y decoders, program/verified circuitry, data registers, andthe like are provided, for example as taught by U.S. Pat. No. 5,890,192,issued Mar. 30, 1999, and assigned to Sandisk Corporation, assignee ofthe present application, which patent is hereby incorporated herein inits entirety by this reference. Related memory system features aredescribed in patent application Ser. No. 09/505,555, filed Feb. 17, 2000by Kevin Conley et al., now U.S. Pat. No. 6,426,893, which applicationis expressly incorporated herein in its entirety by this reference.

The external interface I/O bus 411 and control signals 412 can includethe following:

-   -   CS—Chip Select. Used to activate flash memory interface.    -   RS—Read Strobe. Used to indicate the I/O bus is being used to        transfer data from the memory array.    -   WS—Write Strobe. Used to indicate the I/O bus is being used to        transfer data to the memory array.    -   AS—Address Strobe. Indicates that the I/O bus is being used to        transfer address information.    -   AD[7:0]—Address/Data Bus This I/O bus is used to transfer data        between controller and the flash memory command, address and        data registers of the memory control 450.

This interface is given only as an example as other signalconfigurations can be used instead that provide the same functionality.FIG. 1 shows only one flash memory array 400 with its relatedcomponents, but a multiplicity of such arrays can exist on a singleflash memory chip that share a common interface and memory controlcircuitry but have separate XDEC, YDEC, SA/PROG and DATA REG circuitryin order to allow parallel read and program operations among the arrays.

Data is transferred between the memory array via the data register 404and an external controller via the data registers' coupling to the I/Obus AD[7:0] 411. The data register 404 is also coupled the senseamplifier/programming circuit 454. The number of elements of the dataregister coupled to each sense amplifier/programming circuit element maydepend on the number of bits stored in each storage element of thememory cells In one popular form, flash EEPROM cells each contain one ormore floating gates as charge storage elements. Each charge storageelement may store a plurality of bits, such as 2 or 4, if the memorycells are operated in a multi-state mode. Alternatively, the memorycells may be operated in a binary mode to store one bit of data perstorage element.

The row decoder 401 decodes row addresses for the array 400 in order toselect the physical page to be accessed. The row decoder 401 receivesrow addresses via internal row address lines 419 from the memory controllogic 450. A column decoder 402 receives column addresses via internalcolumn address lines 429 from the memory control logic 450.

FIG. 2 shows an architecture of a typical non-volatile data storagesystem, in this case one employing flash memory cells as the storagemedia. In one form, this system is encapsulated within a removable cardhaving an electrical connector extending along one side to provide thehost interface when inserted into a receptacle of a host. Alternatively,the system of FIG. 2 may be embedded into a host system in the form of apermanently installed embedded circuit or otherwise. The system utilizesa single controller 301 that performs high-level host and memory controlfunctions. The flash memory media is composed of one or more flashmemory devices, each such device often formed on its own integratedcircuit chip. The system controller and the flash memory are connectedby a bus 302 that allows the controller 301 to load command, address,and transfer data to and from the flash memory array. The controller 301interfaces with a host system (not shown) with which user data istransferred to and from the flash memory array. In the case where thesystem of FIG. 2 is included in a card, the host interface includes amating plug and socket assembly (not shown) on the card and hostequipment. The controller 301 receives a command from the host to reador write one or more sectors of user data starting at a particularlogical address. This address may or may not align with a boundary of aphysical block of memory cells.

The flash memory array 400 is usually divided into two or moresub-arrays, herein referenced as planes, two such planes 400 a and 400 bbeing illustrated in FIG. 3. A larger number of planes, such as four oreight, may alternatively be included in the memory array 400. Each planeis shown to have 16 physical blocks 0-15, for convenience ofillustration, while an actual plane will typically include far moreblocks. The block contains the smallest number of memory cells that areerasable at one time, the unit of erase. Each of the planes has its owndata registers 404 a and 404 b, and programming circuits 454 a and 454b, respectively. This allows simultaneous programming of data intomemory cell blocks of each of the planes 400 a and 400 b. Each of theplanes is operable somewhat independently of the other, as a sub-array.

FIG. 4 shows one of the blocks of FIG. 3 to contain sixteen pages 0-15of data, for convenience of illustration, since each block likelycontains more pages. A page includes the smallest number of memory cellsthat are programmable together in one programming operation, aprogrammable unit. Each page in turn stores one or more sectors of datafrom the host to which some overhead data generated by the memorycontroller are usually added. An example of a data sector stored in apage is shown in FIG. 5 to contain user data 441 obtained from the hostplus overhead data 443 that contains information of the user data 441and/or of the physical block in which the data sector is stored. Theamount of user data 441 in a sector can conveniently be 512 bytes ofdata. This unit of storage is particularly useful when the memory systemis used with a host that transfers data to and from the memory in unitsof data sectors, which includes most personal computers. The overheaddata may be in the order of 16 bytes for each 512 bytes of user data.

If the memory system is operated with binary states, where one bit ofdata is stored in each memory cell storage element, one sector of userdata plus overhead data occupies 528 memory cells. If the memory cellsare operated in four states, thus storing two bits of data per cell,only one-half as many cells are required to store a single data sector,or the same number of cells can store two data sectors such as whereeach cell stores one bit from each of two data sectors. Operation with ahigher number of states per storage element further increases the datastorage density of an array.

In some prior art systems having large capacity memory cell blocks thatare divided into multiple pages, as discussed above, data of pages in ablock that are not being updated need to be copied from the originalblock to a new block that also contains the new, updated data that hasbeen written by the host. This technique is illustrated in FIG. 6,wherein two of the blocks of one of the planes of FIG. 3 are shown,blocks 3 and 13 of plane 0, for example. Data within pages 7-10 of theoriginal block 3 are being updated by the four pages of updated datashown. The new data is written into the corresponding pages 7-10 of anunused erased block 13. Unchanged user data from pages 0-6 and 11-15 inthe original block 13 are then copied into corresponding pages of thenew block 13. All pages of the new block 13 are preferably programmed ina single sequence of programming operations. After the block 13 is fullyprogrammed, the original block 3 is erased and placed into an erasedblock pool for later use. The copying of data between the blocks 3 and13, which involves reading the data from one or more pages in theoriginal block and subsequently programming the same data to pages in anewly assigned block, adversely affects the write performance and usablelifetime of the memory array.

With reference to FIGS. 7A and 7B, partial tables show mapping of thelogical blocks into the original and new physical blocks 3 and 13 before(FIG. 7A) and after (FIG. 7B) the updating of data just described withrespect to FIG. 6. Before the data update, the original block 3, in thisexample, stores pages 0-15 of LBN3 in corresponding pages 0-15 of PBN3.After the data update according to FIG. 6, the new block 13 stores pages0-15 of LBN3 in respective pages 0-15 of PBN13. The address translationtable is shown in FIG. 7B to have been updated in this manner. Receiptof a request from the host to read data from LBN3 is then directed tothe physical block 13 (PBN13) instead of the original physical block 3(PBN3).

The LBN of the data in each page may be stored as overhead data in thatpage, as done in some commercial flash memory products. The controllerthen builds a table in the form of that shown in FIGS. 7A and 7B fromthe LBN fields read from the physical pages and the PBNs of those pages.The table may be stored in a volatile memory of the controller for easeof access, although only a portion of a complete table for the entiresystem need be stored at any one time. A portion of the table may beformed immediately in advance of a read or programming operation thatinvolves the blocks included in the table portion.

In other prior art systems that operate differently than described withrespect to FIG. 6, an old/new flag is included as overhead stored withthe user data in each of the pages in order to distinguish the pagescontaining the new data from the pages containing the superceded data.Only the new data are written to the newly assigned block. The data inpages of the original block not being updated need not be copied intothe new block. Data of one logical block is then split between twophysical blocks and is duplicated in part. This requires that morememory blocks be made available for a system having a given memorycapacity. It also requires use of a memory that allows writing a flag tothe old pages without first having to having to erase those pages.

Various flags are typically stored as overhead in the same physical pageas the other associated overhead data, such as the LBN and an ECC field.Thus, to program the old/new flags in pages where the data has beensuperceded requires that a page support multiple programming cycles.That is, the memory array must have the capability for its individualpages to be programmed in at least two stages between erasures.Furthermore, the block must support the ability to program a page whenother pages in the block with higher offsets or addresses have beenalready programmed. A limitation of some flash memories, however,prevents the usage of such flags by specifying that the pages in a blockcan only be programmed in a physically sequential manner. Furthermore,in such flash memories, the pages support a finite number of programcycles and in some cases additional programming of programmed pages isnot permitted. There are many different types of flash EEPROM, each ofwhich presents its own limitations that must be worked around to operatea high performance memory system formed on a small amount of integratedcircuit area.

What is needed is a mechanism of optimally managing data based on hostusage data patterns.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The trend in the development of flash EEPROM systems is to increasesignificantly the number of memory cells, and thus the amount of datastored, in the individual blocks in order to reduce the cost ofmanufacturing the integrated memory circuit chips. A block size ofsomething like 512 or 1024 sectors of data (528 bytes each) iscontemplated, thus having an individual capacity of 270,336 or 540,672bytes of user and overhead data. If only one sector is included in apage, then there are the same number of pages but the trend is also toincrease the amount of data that is programmed as part of oneprogramming operation by including two, or perhaps more, data sectors ineach page, in which case the number of pages in a block that stores agiven number of sectors of data is reduced. But regardless of thedetails of any particular implementation, the existing techniquesdescribed above for updating only a portion of the data in a blockincreases the adverse effect on memory performance and/or capacityutilization as the data storage capacity of the individual blockincreases.

It can be seen that if the data in only a few of the 528 or so pages ofa block are being updated, the existing technique described with respectto FIG. 6 will have a significant increased overhead in terms of theamount of time required to copy the remaining unchanged pages, usuallyone page at a time, from the old to the new block. Although this can bea problem with much smaller block sizes now in use in real time datastorage applications, it becomes worse as the size of the blocksincreases. And if the alternate technique of tagging the old data pagesin the original block is used, the few pages of updated data are writteninto another large block with the likelihood that the remaining pages inthe new block remain unused.

Therefore, according to one aspect of the present invention, at leastone block is provided in each plane of the memory for receiving suchsmall amounts of updates to the data of some or all of the other blocksin the plane. In a memory plane illustrated in FIG. 8, one type of block10 is so designated, identified herein as an E1 block. There is also atleast one type of block (referred to as an E2 block) designated for eachmemory plane that operates differently, as described later. Any ofunused blocks in the plane may be designated as E1 or E2 blocks, andthis designation can be changed from time to time during operation ofthe memory. The designation of E1 and E2 blocks is dependent on theprogramming patterns of the host.

With reference to FIG. 9, use of the E1 block is described. In thisexample, data in pages 7-10 of block 3 are being updated, as in theexample previously described with respect to FIG. 6. But instead ofwriting the updated data to the same range of pages within a new block,they are written in the E1 block in any convenient unused erased pages,usually the next in order. In FIG. 9, the E1 block is shown to bestoring, in its pages 0-2, updated data from three pages of logicalblock 7, and, in its pages 3 and 4, updated data from logical block 2.The most convenient place to store the current pages 7-10 of updateddata from logical block 3 is in the next pages 5-8, respectively, thenext four pages in order. The remaining erased pages 9-15 of the E1block are available to store updated data from pages of other blocks.

At the time of storing the updated data, the original data in pages 7-10of block 3 become obsolete, in this example. When reading the data ofblock 3, therefore, the memory system controller needs to also identifythe updated pages 7-10 from the E1 block and use their data in place ofthat of pages 7-10 in the original block. An address map is maintainedin a fast volatile memory of the controller for this purpose. Data forthe address map are obtained upon initialization of the system from theoverhead data of the pages in at least a portion of the system or otherstored data in the non-volatile memory, including data in the E1 block.This data include the LBN of each page that is commonly included as partof the overhead data of each page. Since the pages are not constrainedto be written in any particular order in the E1 block, the overhead ofeach data page also preferably includes its logical page offset withinthe block. The data of the address map are then updated from theoverhead fields of any data pages that are changed in the E1 block.

It has been assumed so far that there is only one update of any givenpage in the E1 block. This may be the case in some applications but notin others. In the example of FIG. 9, for example, page 8 of the originalblock 3 could be updated a second time, and this second update is alsostored in the same E1 block, in another of the available erased pages.When reading the data stored in block 3, the controller also reads datafrom the headers (overhead data) of the pages within the E1 block,either from a table maintained in controller memory or from the pagesthemselves. The headers of the programmed pages within the E1 block areread in the same direction each time, such as from its highestprogrammed page 8 to page 0, in the example of FIG. 9. In the case ofduplicate updated pages being encountered in the type of memory wherepages are written in sequence, the controller knows that the first to beread in reverse sequence is the most current and subsequently ignoresall other pages in the E1 block that have the same LBN and page offsets.The headers of the pages within the E1 block can also be read duringinitialization of the memory to maintain a complete map.

As a more general, alternate way to identify the most current of twopages having the same LBN and page offset, the overhead of each page mayadditionally contain an indication of its time of programming, at leastrelative to the time that other pages with the same logical address areprogrammed. This allows the controller to determine, when reading datafrom a particular block of the memory, the relative ages of the pages ofdata that are assigned the same logical address. This technique allowsthe updated pages to be written into the E1 block in any order, in amemory system that allows this. It can also make it easier to operate amemory system with more than one E1 block in a single plane. This way ofdistinguishing old from current data is described more fully inaforementioned United States patent application publication no.2002-0099904.

There are several ways in which the time stamp may be recorded in theindividual pages. The most straightforward way is to record, when thedata of its associated page is programmed, the output of a real-timeclock in the system. Later programmed pages with the same logicaladdress then have a later time recorded. But when such a real-time clockis not available in the system, other techniques can be used. Onespecific technique is to store the output of a modulo-N counter as thetime stamp. The range of the counter should be one more than the numberof pages that are contemplated to be stored with the same logical pagenumber. When updating the data of a particular page in the originalblock 3 of FIG. 9, for example, the controller first reads the countstored in the overhead of the page whose data are being updated,increments the count by some amount, such as one, and then writes thatincremented count in the new updated page being stored in the E1 block.If this count is included in a table maintained in a controller memory,the controller reads it from that table. Otherwise, the controller readsthe count from the header of the page being updated. The counter, uponreaching a count of N, rolls over to 0. The number of blocks with thesame LBN is made to be less than N in order to insure that there is apoint of discontinuity in the values of stored counts. This allows thesystem counter to detect the case in which a LBN with a low count valueis more recent than a LBN with a higher count value.

The controller, when called upon to read the data, easily distinguishesbetween the new and superceded pages' data by comparing the time stampcounts in the overhead of pages having the same LBA and page offset. Inresponse to a need to read the most recent version of a data file, datafrom the identified new pages are then assembled, along with originalpages that have not been updated, into the most recent version of thedata file.

An example of the structure of a single sector of data stored in theindividual pages of FIG. 9 is shown in FIG. 10. The largest part is userdata 45. An error correction code (ECC) 47 calculated from the user datais also stored in the page. Overhead data 49, including a field 41storing the LBN and page tag (logical page offset), the time stamp 43and an ECC 50 optionally calculated from the overhead data are alsostored in the page. By having an ECC 50 covering the overhead data thatis separate from the user data ECC 47, the overhead 49 may be readseparately from the user data and evaluated as valid without the need totransfer all of the data stored in the page. Alternatively, however,where the separate reading of the overhead data 49 is not a frequentevent, all of the data in the page may be covered by a single ECC inorder to reduce the total number of bits of ECC in a page. As analternative to using an ECC, other known redundancy techniques can beemployed instead. Additional description of techniques to keep track ofmultiple versions of the same data page is contained aforementionedUnited States patent application publication no. 2002-0099904.

The E1 block is used for updates when the number of pages being updated,for example, by a single host command is small in comparison with thetotal number of pages in the individual block. When a sufficiently largeproportion of the pages of a block are being updated, it is then moreefficient to use the existing technique instead, described with respectto FIG. 6, wherein the updated and unchanged pages are written directlyto a new block with their original page order being maintained. Oneprocess or the other is chosen by the controller, depending upon theproportion and/or absolute number of pages of a block being updated atone time, and perhaps other factors of the operation of the memory atthe time the update is taking place. One such other factor may be whenit is inconvenient to consolidate pages in the new block 13, which maybe designated as the E2 block, in which case the updated data aretemporarily stored in the block E1.

The optimum proportion or number of updated pages that serves as adecision criterion between invoking the two updating techniques maydiffer between memory systems that are constructed and/or operated indifferent ways. But having a fixed criterion is the most convenient toimplement. For example, if the number of pages being updated is lessthan 50 percent of the total number of pages in the block but at leastone page is being updated, the new technique of FIG. 9 is used. If thatproportion is equal to or greater than 50 percent but at least one pageis not being updated, the existing technique of FIG. 6, or somethingsimilar, is used. The decision number may be, for instance, as high as75 percent in some systems, or as low as 25 percent in others. Thecriteria for choosing the decision number, for example, can be thatwhich optimizes the performance (such as the speed of handlingprogramming operations) of the memory system. The number can be storedas a system parameter in order that it may be modified during productconfiguration for system optimization. An algorithm can also be includedin the controller operation to update and optimize the decision numberbased on a history of a current host operations including garbagecollection activity.

Once a decision is made by the controller to direct incoming data to theE1 block, the nature of the programming operation may be detected, afterwriting one or more pages into the E1 block, to be better directed tothe E2 block. An example situation is when sequential write commands arediscovered to be writing sequential pages in a single block, one or afew pages at a time. This can be noted by the controller after a fewsuch pages are written into the E1 block, after which further writes tothe E1 block are stopped and the remaining sequential writes aredirected instead to the E2 block. Those pages already written to the E1block are then transferred to the E2 block. This procedure reduces thelikelihood of having to consolidate the pages of the block E1 as aresult of this programming operation. Alternatively, in a case where thesequential page writes begin in an erased E1 block, that block may beconverted to an E2 block.

FIG. 11A shows the use of the E2 block 13 (FIG. 8) when the number ofpages being updated is higher than the predetermined decision level. Inthis situation, the E1 block 10 is not used. Rather, the updated datasectors of pages P2-P11 stored in an original block 3, as an example,are written directly into the same pages P1-P11 of the E2 block 13,which block has been previously erased. The data sectors of theremaining pages P1, P2 and P12-P15 of the original block 3 that are notbeing changed are then copied into the E2 block 13 in the same pagesnumbers. In most cases, where more than one data sector is stored in apage, all the data sectors of a page are preferably simultaneouslycopied. A next step, as indicated by FIG. 11B, is to erase the originalblock 3 and designate it as the new E2 block for future operations. Thetranslation table of the type illustrated in FIGS. 7A and 7B is updatedto show the changed PBN for the same LBN.

As described above, updated pages of data of one block are preferablystored in pages of the E2 block having the same offsets as in theoriginal block. As an alternative that is suitable for someapplications, however, the system controller can store pages in the E2block without regard for their offsets within the original block. Thepages can, in this alternative, be stored in order beginning with pageP0 of the E2 block. This adopts one characteristic of the E1 block thatis different from the usual blocks but will still not allow more thanone copy of any page of data to be stored in the E2 block. When thisalternative type of E2 block is used, data consolidation may be morecomplex since the out of order pages in the E2 block will be transferredinto pages of another block having the page offsets of their originalblock, in order to combine these updated pages with unchanged pages ofthe original block.

In order to be able to limit the number of blocks in a system that areset aside to serve as E1 blocks, it is desirable that they be usedefficiently so that there are an adequate number of erased E1 blockpages available to satisfy an expected demand for small partial blockupdates. Therefore, an intermittent consolidation takes place of pagesof data of a logical block that are stored in a primary physical blockand the E1 block. This removes at least some of the updated data pagesfrom the E1 block that belong to that logical block, thus making thesepages available for future use. They are consolidated into a singlephysical block.

An example of such an erase consolidation operation (garbage collection)is given in time sequential block diagrams of FIGS. 12A, 12B and 12C. Ineach of these figures, the top diagram represents the use of the pagesof block 3 of the memory array plane of FIG. 8, which initially (FIG.12A) is the primary block storing data of a particular logical block.Data from pages P7-P10 of block 3 have been updated, however, and thosepages of data have been stored in pages P5-P10 of the designated E1block 10 (middle diagram of FIG. 12A). The remaining pages P0-P6 andP11-P15 of block 3 contain valid data. Other pages P0-P4 of the E1 block10 contain updated data from a block other than block 3 of FIG. 8.

As a first step in an erase consolidation operation to free up some ofthe pages of the E1 block, data from the four pages P5-P8 of block 10are copied into pages P7-P10 of the designated E2 block 13 (bottomdiagram of FIG. 12A). Block 13 has earlier been erased. These data arenow stored in the pages of block 13 that have the same address offsetsas they originally did in block 3 before their data were updated. A nextstep is to then copy the valid data pages P0-P6 and P11-P15 from block 3into pages of the E2 block 13, as shown by FIG. 12B. Block 13 thencontains all the pages of data from the original block 3, with data inits pages P6-P10 being updated, in the single physical block 13. Block 3is then (FIG. 12B) erased and designated as the new E2 block for thememory plane of FIG. 8. Many of these steps may be executed in parallel.

Although the data in pages P5-P8 of the E1 block 10 are no longernecessary (FIG. 12B), the data in pages P0-P4 of the E1 block are stillvalid, being updated data of pages of another physical block. Those dataare then copied into pages P0-P4 of the erased block 3, as shown in FIG.12C. Block 3 is then re-designated by the controller as the E1 block,leaving the erased pages P5-P15 for future use to temporarily storepages of updated data in the same manner as described above. Block 10 isthen erased and designated by the controller as the E2 block. The old,superceded pages of data have all been deleted as part of the process.

There are several triggering events that can be used by the memorysystem controller to initiate the erase consolidation operationdescribed above with respect to FIGS. 12A-12C. The most common event iswhen the block that is designated as the E1 block at the moment has acertain proportion of its pages full of updated data. A certain numberof erased pages need to be kept available in the E1 block, that numberdepending upon a number of factors such as the number of blocks usingeach E1 block for updates. It is most beneficial to the E1 block toconsolidate the block that has the most obsolete data pages in the E1block. A single erase consolidation operation then clears the largestnumber of unnecessary pages from the E1 block. There are other criteriathat may also be used to choose the block having data pages in block E1that is to be consolidated, such as the detection of an error in thedata of such a block's data page(s) in the block E1. This minimizes thechance that the occurrence of any subsequent error in the block E1page(s) will swamp its ECC.

Another event that can be used to trigger the erase consolidation ofFIGS. 12A-12C can be when performance of the memory becomes degraded dueto insufficient space in the designated E1 block. When a certain numberof pages of a block are being updated and there are too few erased pagesin the E1 block to store the number of pages being updated, thecontroller preferably writes the updated pages into the E2 or othererased block with the same page offsets as the original data pages beingupdated. This necessarily occurs even though the number of pages beingupdated is less than the predetermined number that would normally callfor use of the E1 block. The valid or non-obsolete data pages are thencopied from the original block into the same E2 or other erased block,to combine all the current data for a logical block into a singlephysical block. This will take more time, and thus adversely affectsystem performance, than if the designated E1 block can be used.Therefore, after this is detected to have happened a predeterminednumber of times, the consolidation operation of FIGS. 12A-12C isperformed in order to free up more pages in the E1 block. Otherwise, thefull advantage of having and using the E1 block are lost. Thepredetermined number of times may be a pre-set parameter or may beadaptively optimized by the memory controller.

Also, when a block of data having updated data pages in the E1 blockneeds to be refreshed, if this data refresh is part of the memory'soperation, its refreshing can include the erase consolidation operationof FIGS. 12A-12C. It can be included as part of other overheadoperations as well, since it is often efficient to do so at that time.Further, as another triggering event, the erase consolidation can bedone when the controller is not otherwise occupied or scheduled to beoccupied for a time sufficient to perform the consolidation operation.Any one, several or all of the factors discussed above may be used toinitiate the erase consolidation operation of FIGS. 12A-12C. Inaddition, although the erase consolidation operation has been describedto consolidate data pages for a single block, the process can berepeated for two or more blocks in order to free up even more pages inthe E1 block. Also, the data pages can be consolidated with those of ametablock. This is conveniently done when the controller is not to becalled upon to perform other functions for a time sufficient to domultiple erase consolidation operations involving the E1 block.

The consolidation operation described with respect to FIGS. 12A-12C usesavailable erased pages in the E1 block because the number of pages beingupdated at one time is less than a pre-set number, such as one-half thenumber of pages in the E1 block, one of the criteria that may be set forusing the block E1. If more than those number of pages are beingupdated, the updated data are written directly into the E2 block, aspreviously described with respect to FIGS. 11A-11B. A differentconsolidation operation occurs when the number of pages of a logicalblock that are being updated at one time exceeds the predeterminednumber, and no other established criteria for using the block E1 exist,but where one or more updated pages of that logical block havepreviously been written into the E1 block. In this case, the updatedblocks are written directly into the E2 block. An operation of thememory system controller that handles this situation is described withrespect to FIGS. 13A-13C.

In the example of FIG. 13A, pages P2-P11 of the data stored in block 3(top diagram) are being updated at one time. Data pages P12-P13 havepreviously been updated, the updated data being stored in pages P5-P6 ofthe designated E1 block 10 (middle diagram of FIG. 13A) of the memoryplane of FIG. 8. As a first step in updating data pages P2-P11, theupdated data is written directly into corresponding pages P2-P11 of thedesignated E2 block 13 (bottom diagram of FIG. 13A). The previouslyupdated pages P12-P13 are also copied into pages P12-P13 of the E2 blockfrom their location in pages P5-P6 of the E1 block.

A next step, illustrated in FIG. 13B, causes the unchanged data in pagesP1-P2 and P14-P15 of block 3 to be copied into corresponding pagelocations of block 13. Block 13 then stores all pages of the currentupdated data. Block 3 is then erased and designated as the E2 block.Remaining updated data from some block other than block 13, which isstored in valid data pages P1-P5 of the E1 block 10, are then copiedinto corresponding pages of block 3, as indicated by FIG. 13C. Block 3is then designated as the E1 block. Block 10 is then erased and becomesthe E2 block for any future operations that need to use it. All of theold, superceded pages of data have been deleted in the process.

The erase consolidation operation illustrated by FIGS. 13A-13C ispreferably initiated in response to updated data pages being written tothe E2 block (FIG. 13A). That response can be immediate, in order tofree up an E2 block right away for future use within the memory plane,or, alternatively, the consolidation can be initiated after some delay.A delay allowing one or a few further programming cycles to take placeafter writing the updated data pages in the E2 block allows any furtherupdates to the data of the logical block initially stored in physicalblock 3 to be included in the consolidation operation. This saves havingto perform such consolidation twice in close succession for the samedata block.

The erase consolidation operations involving the E1 block, as describedwith respect to FIGS. 12A-12C and 13A-13C, have general application tomemory systems used with personal computers, computer servers, personaldigital assistants, sound and video processing devices, and the like. Inmany of these applications, one or just a few data pages of one or justa few blocks of the memory are updated at one time at frequentintervals. An example is the maintenance of a file allocation table(FAT), a common component of many computer systems. The FAT is oftenstored in only one or a few blocks of a single plane of the memory. Atleast one page storing a portion of the FAT table is usually updatedeach time data is written by the host to the memory, and as part of eacherase consolidation operation, and whenever else the allocation of hostdesignated logical blocks to physical memory blocks designated by thecontroller is changed. Another example of frequent data updates is foroverhead data maintained as part of the memory operation. For example,certain information about the usage or characteristics of each memoryblock is kept together in another block. This data is updated nearlycontinuously as the memory is used.

For systems where such frequent updates of significant amounts of datatake place, a small amount at a time, the performance of the memorysystem is improved by designating more than one E1 block for a region ofthe memory that is subjected to these frequent updates. For a range ofLBAs to which the host stores primarily or only such frequently updateddata, an E1 block or metablock can even be dedicated for use with onlythat block. This is done when a resulting improved performance is worththe cost of having to remove one or more additional blocks from generalservice in order to serve as additional or dedicated E1 (dE1) blocks.This is often the case for blocks storing FAT tables, block overheaddata, and the like. The designation of additional or dedicated E1 blockscan result in a substantial reduction in the frequency at which theerase consolidation operation of FIGS. 12A-12C must be performed.

FIG. 14 illustrates an allocation of blocks in one memory plane at oneinstant in time that is different than that of FIG. 8. In addition toblock 10 being designated by the memory controller as a general E1 blockfor the memory plane, block 2 is designated as a dE1 block for updatesonly from block 1. Whenever data of a page of the LBN mapped to block 1is updated and a condition for writing to the block E1 exists (ratherthan to the block E2), the updated data page is written into anavailable erased page of the dE1 block 2. The page within the within thedE1 block 2 that receives the updated data will be the next page inorder in a memory of the type requiring that pages be written into itsindividual blocks in such a sequence. Similarly, the block 4 isdesignated as a dE1 block dedicated to receive updated data of a LBNmapped to block 3, and block 6 is a dE1 block dedicated to the LBNs ofblock 5. The use of three dedicated E1 blocks within a plane is only onespecific example of the principle being described. Only one dE1 blockmay be provided in some applications, or up to one-half of the blocks ina plane may be so designated. Block 13 is designated as the E2 block forthe example plane of FIG. 14.

The continued use of a dedicated E1 block will, of course, cause it toeventually become full. Certain pages of the data block to which an E1block is dedicated can be rewritten multiple times before the E1 blockbecomes full. Each page is written into the next available erased pageof the E1 block, in this example, and its page offset within theoriginal data block stored as part of the overhead data for the block.Shortly before or at the time that any dedicated E1 block becomes full,a consolidation operation takes place to rewrite the data block toinclude the most current pages from its E1 block and any unchanged datapages. An example of this is given in FIGS. 15A and 15B.

In FIG. 15A, the consolidation of data pages from block 3 and its E1block 4, of FIG. 14, into the E2 block 13 is illustrated. In thisexample, the data of pages P0-P1, P5-P9 and P13-P14 is unchanged. Theremaining pages P2-P4 and P10-P12 and P15 have been updated, in thisexample, with the most recent updated pages being stored in the dE1block 4 at respective pages P7, P2, P11, P13, P10, P8 and P12. Theconsolidation process has been begun, in this illustrative example,because all of the dE1 block 4 pages have been programmed except thehighest two pages P14 and P15; the dE1 block has almost run out ofspace. The unchanged pages in original data block 3 and the most recentupdated pages in dE1 block 4 are then assembled by a programmingoperation into the E2 block 13. Each such page is written into an E2block page having the physical offset of the page. That is, although theupdated pages are temporarily stored in the dE1 block in the order theyare updated, rather than in their respective physical page locations,the most recent updates of pages from the original data block 3 arecopied into the pages of the E2 block 13 having locations correspondingto their addressed offsets. As shown in FIG. 15B, the blocks 3 and 4 arethen erased, one being designated as the E1 block dedicated to the newdata block 13 and the other becoming the E2 block for the memory plane.

However, it is not required that the data pages in the E2 block 13 havethe same address offsets as the pages that are updated or copied. It issufficient that they remain in the same relative order. For example, thefirst data page P0 may be stored in the E2 block 13 of FIG. 15A in thirdphysical page from the left instead of the left most physical page. Theremaining data pages are then positioned in order of their logicaladdresses within the block 13, wrapping around with the last pages P14and P15 stored in the left most two pages of the E2 block 13. When suchpage shifting is utilized, the page tag 41 (FIG. 10) of the user dataoverhead can be used to keep track of the offset of the data pageswithin the E2 block.

The designation and use of the additional E1 blocks in the memory planeof FIG. 14 may be programmed into the memory system controller firmwareto occur when it is desirable to have additional E1 blocks dedicated tooperate with a plurality but less than all the LBNs mapped into theplane. The LBNs chosen to have individual associated E1 blocks are thoseto which the host is expected to frequently update its data.Alternatively, the controller firmware can dynamically designate dE1blocks that are each associated with only one other LBN in response tothe way that the memory is actually used. For instance, when data isbeing written to an LBN by the host in only one or a smaller than normalnumber of sectors per host command, that LBN may be assigned its own dE1block. Additionally, a dE1 block may be assigned to those LBNs where thedata is continuously being overwritten. The use of dE1 blocks reducesthe frequent consolidation of data pages out of the general plane blockE1.

As another example of when the need for a dE1 block exists, a muchhigher use of the consolidation process of FIGS. 12A-12C by a particularblock of data than by other blocks can cause an unused block of theplane to be designated as an E1 block dedicated to operate with the LBNof the frequently updated data. In order to optimize performance, it ispreferable to dedicate a block dE1 to the block being frequentlyconsolidated. An example of a process for the controller firmware todetermine when an E1 block should be dedicated to a given LBN as a dE1block is to maintain counts of (1) the number of host commands forwriting to the given block which cause a write to the E1 block, (2) thetotal number of writing operations to the given block and/or (3) thenumber of sectors with the same logical address that are written to theE1 block. When the ratio of these counts exceeds a predetermined value,then the dedicated block dE1 is established. The consolidation operationof FIGS. 15A and 15B then keeps the E1 block associated with eachlogical block containing such data.

As another example of dynamically establishing dE1 blocks, the memorycontroller can be programmed to distinguish frequently updated types ofdata from less frequently updated types of data, and direct such data tothe appropriate blocks. For example, the memory controller can recognizewhen a single sector of data is being sent by the host with individualcommands, typical of entries for a FAT table that are frequentlyupdated, as compared with the host sending multiple sectors of data witha single command, typical of user data that is not so frequentlyupdated. When single sectors of data are received, they are then mappedto the physical block(s) to which a dE1 block is dedicated. Whenmultiple sectors of data are received by the memory system as a unit,they are sent to data blocks that share an E1 block with other datablocks. This non-dedicated E1 block contains data from multiple LBNs.

The techniques of the present invention may also be applied to memoryarchitectures having one or multiple planes that are logically dividedinto zones but the use of zones is not necessary for implementing thepresent invention. In the case of multiple planes, the individual zonesextend across the planes. Metablocks may or may not be used. An exampleof a memory system defining logical zones across multiple planes isschematically shown in FIG. 16. Four planes 0-3 are shown, althoughfewer or more planes may be included in the memory system. Each planecontains a large number of blocks, a portion of which is indicated bythe rectangles in FIG. 16. Each block includes a number of pages ofdata, as indicated for one of the blocks 61, as described above for theother memory systems. A difference here is that the planes are furtherdivided into zones, where each zone includes a given number of blocksfrom each of two or more of the planes. For example, with reference toFIG. 16, zone 0 includes a number of blocks from each of planes 0-4,zone 1 another group of blocks from each of the planes, and so on. Theblocks in each plane within a zone usually occupy the same contiguousset of physical block addresses but this is not required. A distinctrange of host logical addresses is mapped into each zone.

The unit of operation of the memory system of FIG. 16 is preferably ametablock. A metablock includes, in this example, one block from eachplane that are logically connected together to form the metablock. Inthis case, each metablock is formed within a single zone. One metablockis shown in FIG. 16, within zone 1, formed of blocks 63, 64, 65 and 66,as an example. Characteristic operations of a metablock includesimultaneous erasure of all the blocks within the metablock, andsimultaneous programming and reading of one or more pages from eachblock of the metablock. This increased parallelism significantlyincreases the performance of the memory system. The identity of theindividual blocks within the various metablocks can be maintained as afixed or dynamic linked list, array table and the like, in anyconvenient location within the system. Usually, overhead data storedalong with user data of each page will include an address, logicaland/or physical, sufficient to identify the plane, zone and block inwhich the page resides, as well as an offset of the page within thatblock. An address map is then created within a memory of the controllerby the controller reading these address fields of the page overheaddata. This is usually done for part of the memory at a time, preceding aprogramming, reading or erasing operation directed to that part of thememory. In the case of a system that is not divided into zones,individual metablocks can be formed from blocks throughout the entireavailable physical address space of the multiple planes.

One or more blocks within each zone can be allocated for use as theblock(s) E1 and block(s) E2 for the other blocks in the zone. In theexample illustrated in FIG. 16, zone 1 is provided with one block E1.The writing of a partial block of data to any of the metablocks withinzone 1 will then be directed to the block 69 when that write operationsatisfies the criteria for use of the block E1. More than one block E1will usually be required for each zone, depending upon the size of thezone. Indeed, one or more metablocks can be allocated in each zone forthe E1 function, as illustrated in FIG. 17, where blocks E1 a, E1 b, E1c and E1 d, one from each of the planes 0-3, form a metablock withinzone 1. In either of the cases of FIG. 16 or 17, one or more metablocksE2 are allocated for each zone. Alternatively, a pool of metablocks canbe provided somewhere in the system to serve the E1 and E2 blockfunctions for all zones, such as by grouping them in a single zone. Ametablock E1 can also be dedicated to a single other metablock that isreceiving frequent writes. Indeed, the above description for a singleblock E1, such as the consolidation of FIGS. 12 and 13, canalternatively be implemented with a metablock E1. The size of the blockunit does not alter the basic processes. The use of metablocks for E2sis usually preferred to a single block but the use of single blocks forE1s may be preferred to metablocks for efficiency. It should also benoted that the description involving the use of metablocks in a singlezone of a multiple zone array also applies when the entire arrayincludes only one zone.

In a typical allocation of physical blocks E1, dE1 and E2 for receivingupdated data pages within discrete ranges of logical block addresses, anumber of such blocks are allocated for use with each of two or morenon-overlapping sets of contiguous logical block addresses, such astypically occurs when the system has its blocks or metablocks organizedinto the zones described above. The same rules are then mostconveniently applied with each set of logical block addresses as to whenand how their allocated E1, dE1 and E2 blocks or metablocks are used.

However, the use of any or all of the physical E1, dE1 and E2 blocksneed not follow such constraints. For example, the rules of when and howthese special blocks are used can be different for one range of logicalblock addresses than for another range. This allows recognition ofdifferent typical host usage patterns or types of data that are storedin different ranges of host logical addresses. Further, the range oflogical block addresses to which a particular set of E1, dE1 and E2blocks is dedicated need not be entirely contiguous. One range oflogical block addresses can even be made to overlap with another range,with the rules for using the E1, dE1 and E2 blocks dedicated to eachoverlapping range being different. In this latter case, programming bythe host of data with logical block addresses within the overlappingranges are eligible for storage in one of two or more sets of physicalE1, dE1 or E2 blocks, depending upon which set of rules is satisfied bythe host operation. Preferably, the rules are set so that any oneprogramming operation in an overlapping logical address range iseligible for storage in only one of the possible sets of E1, dE1 or E2blocks.

FIG. 18 shows an example assignment of physical E1, dE1 and E2 blocks tological block addresses. Among the four logical blocks LBN{x} throughLBN{x+3} having sequential logical addresses that are illustrated,LBN{x}, LNB{x+1} and LBN{x+2} share a common E1 block for storingupdated data satisfying the criteria for use of an E1 block while theyare each mapped into separate E2 blocks for storing updated datasatisfying the criteria for use of an E2 block. The ranges of logicalblock addresses designated to use specific E1 and E2 blocks may be thesame, different with some overlap or mutually exclusive. The memory maythen adapt to host usage. For example, in the case of logical addressranges receiving frequent single data sector updates, they can be mappedto E1 or dE1 blocks but not an E2 block since the update of enough dataat one time to make an E2 block useful is unlikely.

Data stored in an E2 block, when a portion is further updated, arestored in an E1 block designated for the same data logical addresses. Ofcourse, updated data having logical addresses designated for an E2 blockcan be stored in an E1 block without first having to store data of thatlogical address within the E2 block. The selection of the E1 or E2 blockfor storing updated data is dependent upon the criteria discussed above.

The flowchart of FIG. 19 shows an exemplary operation of a flash memorysystem that utilizes the blocks E1, dE1 and E2 discussed above in amanner that dynamically responds to patterns of host operation tooptimize performance of the memory system. The process begins each timethe memory system receives a write command from the host system to whichit is connected, as indicated at 101. The write command includes the LBNof the data, the number of sectors of data to be written, and the like.The LBN will cause the data to be mapped into a block of a memory planeor into a metablock extending across multiple planes, depending upon thestructure and operation of the particular memory array being programmed.A first step 103 checks whether an existing E2 block or metablockassociated with the received LBN has room for the number of data sectorsbeing programmed. If so, a next step 105 determines whether the datasectors of the current write operation are a continuation of a previouswrite operation with sequential addresses. If so, the data areprogrammed into the existing E2 block, as indicated by a step 107.

But if it is determined in the step 105 that the new write is not ofsectors that are a continuation of a previous sequence of sectors, it isthen determined in a step 109 whether the gap of logical sectoraddresses involves a small number of sectors, such as one or just a few.If less than some preset number of sectors, then these unchanged datasectors are copied into the E2 block in order, as indicated by a step111, and the new data sectors are written to the E2 block per the step107. This copying of a few sectors of unchanged data into the existingE2 block may be optimal rather than treat the subsequent write astotally disconnected from the prior write because of a gap of a smallnumber of sectors.

But if the logical address gap is larger than the preset number ofsectors, then a next step 113 considers whether a new E2 block should becreated for an LBN range that includes the pending write operation. Thestatistics considered can include an analysis of stored or recent writetransactions, or may be as simple as determining whether the number ofsectors of the current write operation is greater or not than a fixed ordynamically determined threshold number. This threshold number may be,for example, less than the number of data sectors stored in a block butmore than one-half or three-quarters of a block's capacity. If it isdetermined from the defined statistics to create a new E2 block, this isdone in a step 115 and the data of the pending write are then programmedinto the new E2 block in the step 107. The process for allocating a newE2 block is explained below with respect to the flowchart of FIG. 20.

This discussion is based upon the determination being made in the step103 that there is room in an existing E2 block for the number of datasectors of the pending write operation. If there is not enough room,however, the processing jumps to the step 113 to determine whether a newE2 block should be created.

If it is determined in the step 113 that a new E2 block should not becreated for the data of the pending write operation, it may likely bebecause the number of sectors is less than (or equal to) the presetthreshold number used in the step 113 and thus more appropriatelywritten to an E1 block. In a next step 117, therefore, it is determinedwhether an existing dE1 block exists for an LBA range in which thecurrent data sectors reside. If so, these data sectors are programmedinto that dE1 block, in a step 119. But if not, it is then determined ina step 121 whether a new dE1 block should be created. This determinationmay be based upon an analysis of stored operations, logical or physical,or may be based upon instantaneous operations. The statistics consideredmay include the occurrences of garbage collection operations, number ofE1 blocks created or the number of non-sequential single sector writeoperations within a given LBA range. A dE1 block is dedicated for acertain block when the number and frequency of updates of data in thatcertain block are much higher than is typical for a majority of theblocks in the system. If a dE1 is to be allocated as a result, this isdone in a step 123 in accordance with the flowchart of FIG. 20.

But if there is no room in an existing dE1 block and it is determinednot to allocate another, then room in an existing E1 block associatedwith the LBA of the pending write operation is sought, in a step 125. E1blocks may be individually limited to storing data sectors of a specificrange of LBAs in order to make them easier to manage, such as providingone in each plane as described above. Alternately, E1 blocks may storedata with LBAs from anywhere within the array. If there is enough spacefor the data, then, in a next step 127, that data is written into the E1block associated with the LBA of the data.

If, on the other hand, the E1 block associated with the LBA of the datadoes not have room, space is sought in another E1 block, as indicated bya step 129. If such space exists, a decision is then made as to whetherto expand the range of LBAs handled by the other E1 block to include theLBA of the current data. Depending upon usage patterns of the host, itmay be better either to store data with any LBAs in any of several orall of the E1 blocks in the system, or to strictly limit each E1 blockto a set range of LBAs. If it is decided to write the data to another E1block, this is done in the step 127. However, if it is decided not towrite the data to another E1 block, then a new E1 block is allocated,per step 131, and the data written into it in the step 127.

A routine for allocating a new block in any of the steps 115, 123 or 131is shown by the flowchart of FIG. 20. If it is determined in an initialstep 133 that a memory block is available in the pool of erased andunused blocks, then such a block is assigned in a step 135 to be an E2,dE1 or E1 block, depending upon which of the respective steps 115, 123or 131 of FIG. 19 is being executed. However, if no such block isavailable, an existing E1, dE1 or E2 block is deallocated and reassignedthe new role. The remaining steps of FIG. 20 decide whether it is an E1,dE1 or E2 block that is deallocated for this purpose. The principleapplied in this example is to deallocate a block that is the least usedand useful.

If a new E1 block is being created, when the processing of FIG. 19 is inthe step 131, it is then determined, in a step 139 of FIG. 20, whether amaximum number of E1 blocks already exists. This number may be set or,preferably, changes in order to optimize usage of all three of thesetypes of blocks. The total number of E1, dE1 and E2 blocks that aredesignated is generally limited by the number of extra blocks providedin the system over what is required to respond to its full logicaladdress space. If it is determined that a maximum number of E1 blockshave been created, then a next step 141 deallocates an existing E1 blockand, in the step 135, this block is designated as the new E1 block.However, if it is determined in the step 139 that the maximum number ofE1 blocks have not been created, it is then decided in later stepswhether to deallocate a dE1 block or an E2 block for the new E1 block.The new E1 block may be limited for use with a specified range of LBAsor may cover the entire memory array.

If a new dE1 block is being created (step 123 of FIG. 19) instead of anE1 block, as determined by a step 143, a question resolved in a step 145is whether the maximum allowable number of dE1 blocks already exists. Ifso, one of them is deallocated in a step 147 and assigned as the new dE1block in the step 135. If not, a step 149 is reached wherein usagepattern statistics are used to determine whether an existing dE1 blockshould be deallocated. The statistics may include a measure whether theexisting dE1 block is stale.

The step 149 is also reached from the step 143 when neither a new dE1nor a new E1 block is being created, and from the step 139 when themaximum numbers of E1 blocks have not been created. If it is determinedin the step 149 to deallocate a dE1 block, then this is done in the step147 and that block is reallocated in the step 135 as one of the new E1or dE1 blocks being created. But if an existing dE1 block is not to bedeallocated, then step 151 is reached wherein an E2 block isdeallocated, followed by assigned that block as the new E1 or dE1 block.When assigned as a dE1 block, it may be assigned a LBN range thatexceeds that of a single other physical block.

Although the invention has been described with respect to variousexemplary embodiments, it will be understood that the invention isentitled to protection within the full scope of the appended claims.

It is claimed:
 1. A method of writing data into a non-volatile memorysystem of a type having blocks of memory cells that are simultaneouslyerasable and which individually store a given number of host units ofdata, comprising: designating a first of the blocks for storage of anumber of units of data with sequential logical addresses that is lessthan a pre-set proportion of the given number, the pre-set proportionbeing less than the given number, thereafter responding to a pluralityof successive host commands to write a number of units of data less thanthe pre-set proportion of the given number that have sequential logicaladdresses by writing their data into the first designated block withsequential physical addresses, and responding to host commands to writea number of units of data having sequential logical addresses that isequal to or in excess of the pre-set proportion of said given number bywriting their data into a block other than the first designated block.2. The method of claim 1, which additionally comprises, prior to writingdata of the plurality of successive host commands: determining whetheror not the successive host commands individually include a number ofunits of data having sequential logical addresses less than the pre-setproportion of said given number.
 3. The method of claim 2, wherein thepre-set proportion is set within a range of 25-75 percent of said givennumber.
 4. The method of claim 1, wherein the non-volatile memory cellsare organized into multiple sub-arrays and said blocks of memory cellsinclude memory cells of two or more of the sub-arrays.
 5. The method ofclaim 1, wherein the pre-set proportion is set within a range of 25-75percent of said given number.
 6. A method of writing data into anon-volatile memory system of a type having blocks of memory cells thatare simultaneously erasable and which individually store a given numberof host units of data, comprising: designating at least a first one ofthe blocks to store a number of units of data having sequential logicaladdresses that is less than a pre-set fraction of said given number,thereafter responding to a plurality of successive host commands toindividually write units of data into the memory system by determiningwhether a number of the units of data with sequential logical addressesis less than the pre-set fraction, and, if so, by writing the data intothe first dedicated block, and responding to host commands to writeunits of data having a number of sequential logical addresses that isequal to or in excess of the pre-set fraction of said given number bywriting the data into a block other than the first dedicated block. 7.The method of claim 6, wherein the non-volatile memory cells areorganized into multiple sub-arrays and said blocks of memory cellsinclude memory cells of two or more of the sub-arrays.
 8. The method ofclaim 6, wherein the fraction is set within a range of 25-75 percent ofsaid given number.
 9. A method of operating a non-volatile memory systemin response to commands received from a host to individually writelogically addressed units of data therein, the memory system havingmemory cells grouped into blocks of memory cells that are simultaneouslyerasable and which individually store a given number of units of data atindividual physical addresses, the logical addresses of received unitsof data being mapped within the memory system into correspondingphysical addresses where the received units of data are stored,comprising: allocating a first one of the blocks to store units of datahaving a number of sequential logical addresses less than apre-determined fraction of said given number, allocating a second one ofthe blocks to store units of data having a number of sequential logicaladdresses equal to or in excess of the fraction of said given number, inresponse to receipt of a command to write data having a number ofsequential logical addresses less than said fraction, determiningwhether the first block has sufficient erased capacity to store thereceived data and, if so, writing the received data into sequentialphysical addresses of the first block, and in response to receipt of acommand to write data having a number of sequential logical addressesequal to or in excess of said fraction, determining whether the secondblock has erased capacity to store the data and, if so, writing the datainto sequential physical addresses of the second block.
 10. The methodof claim 9, additionally comprising: in response to receipt of thecommand to write data having a number of sequential logical addressesless than said fraction, if the first block does not have sufficienterased capacity to store the received data, allocating a third one ofthe blocks to store units of data having a number of sequential logicaladdresses less than a fraction of said given number and then writing thereceived data into sequential physical addresses of the third block, andin response to receipt of the command to write data having a number ofsequential logical addresses equal to or in excess of said fraction, ifthe second block does not have sufficient erased capacity to store thereceived data, allocating a fourth one of the blocks to store units ofdata having a number of sequential logical addresses equal to or inexcess of the fraction of said given number and then writing thereceived data into sequential physical addresses of the fourth block.11. The method of claim 10, wherein the fraction is set to be within arange of 25-75 percent of said given number.
 12. The method of claim 9,wherein the non-volatile memory cells are organized into multiplesub-arrays and said blocks of memory cells include memory cells of twoor more of the sub-arrays.
 13. The method of claim 9, wherein thefraction is set to be within a range of 25-75 percent of said givennumber.
 14. A method of writing data into a non-volatile memory systemof a type having blocks of memory cells that are simultaneously erasableand which individually store a given number of host units of data,comprising: designating at least a first one of the blocks to store anumber of units of data received by the memory system with individualones of multiple write commands that have sequential logical addressesless than a pre-set fraction of said given number, responding to thereceipt of multiple commands by the memory system to individually writeone or more units of data thereinto by, for individual commands, (a)determining whether the command specifies the writing of a number ofunits of data having sequential logical addresses that is less than thepre-set fraction, and (b) determining whether the first block has enougherased capacity to store the number of units of data provided with thecommand, wherein when both of conditions (a) and (b) above aredetermined to exist, thereafter writing the units of data into the firstblock, but when either one of conditions (a) or (b) above is determinednot to exist, writing the units of data into one of the blocks otherthan the first block.
 15. The method of claim 14, wherein the pre-setfraction is within a range of 25-75 percent of said given number. 16.The method of claim 14, additionally comprising: designating at least asecond one of the blocks to store a number of units of data received bythe memory system with individual ones of multiple write commands thathave sequential logical addresses equal to or greater than the pre-setfraction, and responding to the receipt of multiple commands by thememory system to individually write one or more units of data thereintoby additionally, for individual commands, (c) determining whether thecommand specifies the writing of a number of units of data greater thanthe given number, wherein when neither of the conditions (a) nor (c)above exist, writing the units of data into the second block, withoutregard to whether condition (b) exists or not, but when the condition(c) above is determined to exist, writing the units of data into one ofthe blocks other than the first or second blocks.
 17. The method ofclaim 16, wherein the pre-set fraction is set to be within a range of25-75 percent of said given number.
 18. In a non-volatile memory systemhaving memory cells grouped into blocks of memory cells that aresimultaneously erasable and which individually store a given number ofunits of data at individual physical addresses, the logical addresses ofreceived units of data being mapped within the memory system intocorresponding physical addresses where the received units of data arestored, a method of operation in response to received commands toindividually write logically addressed units of data therein,comprising: designating a first one of the blocks to store units of datahaving a number of sequential logical addresses that is less than apre-determined fraction of said given number, designating a second oneof the blocks to store units of data having a number of sequentiallogical addresses that is greater than the fraction of said givennumber, providing at least another one of the blocks that is fullyerased, and in response to receipt of a command to write data into thememory system, identifying the number of units of the data that havesequential logical addresses, determine whether the number of such unitswith sequential logical addresses are less than the fraction, and, ifso, writing the data to the first of the blocks, but if the amount ofdata is not less than the fraction, then writing the data to the secondof the blocks if there is sufficient capacity therein, but if there isnot sufficient capacity in the second of the blocks, writing the data tothe fully erased block.
 19. The method of claim 18, wherein thepre-predetermined fraction is set to be within a range of 25-75 percentof said given number.